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Forestry is the science of managing forest resources for human benefit. The practice of forestry helps maintain an adequate supply of timber for the manufacture of lumber, plywood, paper, and other wood products. It also includes the management of such valuable forest resources as water, wildlife, grazing areas, and recreation areas.

In general, forests provide the greatest benefits when they are managed with the goal of providing several benefits at once. This concept is called multiple use forest management. In the United States, it is applied in national forests, most state forests, and many private forests. In addition to furnishing timber, these forests may provide water for communities; food and shelter for wildlife; grazing land for livestock; and recreation areas for campers, hikers, and picnickers.

In some forests, however, the importance of one resource may outweigh that of others. For example, companies that manufacture wood products manage their forests primarily for maximum timber production. Or a forest may be protected as a park or as a wilderness or recreation area.

Most countries with forests have at least one government agency to manage forest lands and conduct research. The agency may be an independent government authority. Or it may be part of the nation's park service or agricultural service.

This article discusses the scientific management of forest resources. For information on the various products made from trees, see Forest products. For a discussion of forest ecology, see Forest.

Managing timber resources

The goal of managing timber resources is to achieve an approximate balance between the annual harvest and growth of wood. This balance, called a sustained yield, ensures a continuous supply of timber. It is achieved by managing forests so they have areas of trees of equal yield for each age group, from seedlings to mature trees. The science of harvesting and growing crops of trees for sustained yield is called silviculture. The practice of silviculture requires that foresters know how various species of trees grow in different climates and soils, and how much sunlight and water the trees need. Foresters also use the science of genetics to breed trees that have improved growth rates and greater resistance to diseases and pests.

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Harvesting. There are four silvicultural methods used in the harvest of timber: (1) clearcutting, (2) seed tree cutting, (3) shelterwood cutting, and (4) selection cutting. Each method is designed to provide an environment that favors the establishment of certain kinds of trees. New trees grow from seeds produced by the remaining or surrounding trees, from sprouting stumps or roots, or from seeds or seedlings that foresters plant.

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Clearcutting is the removal of all the trees in a certain area of a forest. It is generally used to reestablish a stand (large group of trees) that is more even in age, by removing a mature one. Clearcutting is also generally used when a forest is to be replaced by planting or by sprouting stumps. Clearcut areas must be large enough to prevent surrounding forests from affecting young trees growing within the clearcut opening.

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Seed tree cutting resembles clearcutting, but foresters leave a few trees widely scattered in the harvested area to provide a natural source of seeds. These seed trees are removed after the new stand is established. Seed tree cutting can be used with various pines, including loblolly pine and longleaf pine.

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Shelterwood cutting involves harvesting timber in several stages over a period of 10 to 20 years. Foresters establish a new stand as the old one is removed. Shelterwood cutting can be used with such trees as oak, ponderosa pine, and white pine, which require shade during their first few years of growth. It also allows the growth of some trees in a stand to continue after the majority of the trees have ceased growing well.

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Selection cutting is the harvesting of small patches of mature trees to make room for younger trees and new growth. The trees are removed on the basis of their size and nearness to other trees. However, foresters leave many larger trees standing to produce seeds. Selection cutting leaves only small openings in a forest, and so it works best with trees that grow well in shade. Such trees include American beech, hemlock, and sugar maple. Forests may be harvested by selection cutting every 15 to 30 years.

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Planting. Foresters plant new timber crops by a process called artificial reforestation. They either plant seeds directly in the harvested land, or they raise seedlings in a nursery and transplant these young trees in the forest. The process is called afforestation when these methods are used to plant trees on land that was never covered by a forest.

Direct seeding works best on cultivated land or on land where a timber crop has been destroyed by fire. The seeds are treated with a chemical repellent, which discourages animals from eating them, and they are sown sometime between late autumn and early spring. Airplanes or helicopters are generally used to scatter the seeds, but seeds may also be placed in the ground with hand tools. About 30,000 seeds per acre (75,000 per hectare) are usually sown to assure an adequate crop.

Forests are planted with seedlings in late winter or early spring, before the buds of the seedlings have opened for the growing season. Seedlings grow in a nursery for one to four years before being transplanted in the forest. Foresters generally plant about 800 trees per acre (2,000 per hectare), using hand tools or various planting machines. A person can plant about 1 acre (0.4 hectare) a day by hand—about as much land as can be planted by machine in an hour.

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Tree improvement involves breeding trees for superior growth rates and increased resistance to diseases and pests. Foresters begin this process by searching forests for the straightest and fastest-growing trees of the species. Such trees, sometimes called supertrees, must also have high-quality wood and be healthy and free of harmful insects and other pests. Tree improvement programs have been used for such species as black walnut, Douglas-fir, and loblolly pine.

After foresters find a superior tree, they take cuttings, called cions, from its branches. The cions are brought to a nursery and grafted (joined) to the roots of 2-year-old trees (see Grafting). The cions receive nutrients through the roots of the young trees but keep the characteristics of the tree from which they were cut. Foresters may use the grafted cions in reforestation. Or they may take pollen from the male flowers to pollinate female flowers of cions from other superior trees. The foresters keep careful records of the cions used for each pollination.

After pollination, the female flowers yield seeds that are planted in the nursery to produce seedlings. Foresters transplant the seedlings into special plantations and closely measure the growth of the trees. If the trees from a particular set of parents appear to be developing into supertrees, the seeds from those parents may be produced commercially for reforestation.

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Community forestry, also called social forestry, is a system of forest management that treats woodlands as a communal resource. In some regions, including parts of North America and northwestern Europe, forests have been set aside for community use for hundreds of years. The idea is newer to developing countries. But rural communities in many such countries have learned to practice community forestry to provide themselves with fuel wood and timber and to increase their food supply.

Community forestry takes many forms. In village woodlots, trees are grown for firewood on any spare patches of land. Agroforestry involves techniques that produce trees in combination with crops, animals, or other products. In intercropping, cereals, vegetables, and fruit are grown between rows of newly planted trees until the trees grow too tall and overshadow them. Silvipasture involves managing tree growth through controlled forest grazing by animals. Multiple-product forestry utilizes techniques designed to increase the yield of fruit, game, honey, and other forest commodities in addition to timber.

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Managing other forest resources

Water. All forests grow within watersheds—that is, regions that supply water for rivers and streams. The soil of forests collects water by soaking up rain and melted snow. Watershed management largely involves keeping forest soil porous so it can absorb a maximum amount of water. The soil of a forest is covered by a spongy layer of leaves and twigs, called litter. The action of earthworms, insects, rodents, and decaying roots creates open spaces within the soil. When rain or snow falls, the water fills these spaces and is absorbed by the litter. Much of the water is used by plants, and some flows underground and then into rivers, streams, and wells. Proper forest harvesting reduces the water lost to evaporation and so increases the underground supply and stream flow of water.

If forest soil becomes too hard and nonporous, water flows over the surface of the ground, carrying mud and other materials into nearby streams. This runoff damages other soil, pollutes the water of the streams, and may even cause flooding.

Foresters help keep soil porous in several ways. They reforest harvested areas quickly to assure a continuous supply of litter. They regulate livestock grazing to maintain a good cover of grass and to prevent the animals from packing down the earth. Foresters also make sure that truck roads built for logging operations are carefully designed to prevent damage to the soil.

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Wildlife. Forests provide homes for a wide variety of wildlife, including bears, birds, deer, fish, foxes, and rodents. Wildlife management involves maintaining a balance between the number of animals in a forest and the supply of food, water, and shelter.

Dense forests of old, tall trees provide good homes for birds, insects, and such climbing mammals as raccoons and squirrels. But the shade in such forests prevents the growth of enough herbs, shrubs, and small trees to feed deer and other large animals that live on the ground. However, openings made in the forest during the timber harvest allow more sunlight to reach the forest floor. New plants sprout in the clearings, providing food for wildlife. Hollow trees may be left in large openings to serve as dens and nesting places.

Wildlife management also involves controlling animal populations by regulating hunting. During food shortages caused by overpopulation of wildlife, animals may damage trees by feeding on bark, buds, and twigs.

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Grazing land. Many forests in dry areas have widely spaced trees with heavy growths of grass and shrubs in-between. Farmers often graze livestock in such areas. The use of rangeland must be carefully regulated to prevent overgrazing, which can damage watersheds. Foresters preserve grasslands chiefly by making sure that livestock roam over the entire range. They also control the number of livestock in a given area, thus preventing the animals from using too much grass in any one area. Foresters sometimes fence off rangeland into many pastures and rotate the grazing among them. To keep livestock moving on open ranges, watering holes may be developed at scattered locations. Placing salt licks away from the water also contributes to better range use.

In addition to controlling overgrazing, foresters maintain grasslands through cultivation. For example, they may control brush, weeds, and poisonous plants with chemicals and then sow the area with seeds. Foresters also may restrict grazing on some land for a year or more to allow new grass to grow there.

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Recreation areas. The scenic beauty and natural resources of forests provide opportunities for many recreational activities, including camping, hiking, fishing, and hunting. Millions of people visit regional and national forests annually. Many forest products companies also open areas of their woodlands to the public, chiefly for hunting and fishing. Privately owned wooded areas also provide recreational benefits.

Many areas of national and regional forests are managed primarily for recreation. Foresters carefully plan these areas to provide maximum benefits to visitors with minimum harm to the forests. Before developing a campground, for example, foresters study such factors as the terrain, the amount of shade, and the availability of water in the area. They can then install picnic tables, cooking equipment, electrical outlets, plumbing, roads and trails, and parking areas without seriously upsetting the ecological balance of the forest.

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Fire and forests

Most scientists consider forest fires an essential natural process. Although fire can cause great destruction, it produces great ecological benefits. Perhaps the leading benefit of fire is that it recycles nutrients, substances that plants need for growth. Fire also clears areas of forest to allow new tree growth. To take advantage of such benefits, foresters permit certain types of fires to burn. Such blazes, called prescribed fires, may be started by lightning or set by fire crews. Prescribed fires must meet certain conditions. For example, they must pose no danger to human lives or buildings.

Other fires, especially those that endanger lives or property, are referred to as wildfires. Wildfires are generally fought quickly and aggressively. Most are caused by human beings. They may be started accidentally or deliberately. Lightning strikes also cause some wildfires. During dry seasons, when fires can easily start, foresters may close a forest to the public to reduce the danger of fire. Foresters may watch for fires from lookout towers, or they may patrol forests by airplane.

To extinguish a wildfire, firefighters must remove the blanket of fuel made up of fallen leaves, twigs, and other decaying material from the forest floor. Firefighting crews spray water or chemicals on the burning area to cool the fire and slow its progress. They then can get close enough to the flames to dig a fireline, also called a firebreak. Firefighters start a fireline by clearing all logs, brush, and trees from a wide strip around the fire. Then they scrape away the litter and some of the soil with axes, shovels, or bulldozers. Firefighters called smoke jumpers may parachute from airplanes or helicopters to dig a fireline in an area that is difficult to reach by land.

After creating a fireline, the firefighters may set backfires to burn the area between the line and the forest fire itself. Backfires remove additional fuel and widen the fireline to help stop the spread of the flames. After a fire dies, the firefighters clear any flammable material from the edge of the burned area. This action prevents the material from smoldering and starting new fires.

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Protecting forest resources

The full benefits of forest resources can be obtained only if timber is protected from diseases and insect pests. Many countries have passed legislation designed to protect forest resources in other ways.

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Diseases and pests. Most tree diseases are caused by fungus infections. Diseases attack trees chiefly by clogging the flow of sap, killing the leaves, or rotting the roots or wood. Destructive tree diseases include beech bark disease, chestnut blight, Dutch elm disease, oak wilt, and stem blister rusts that affect pines. Such diseases are often accidentally transported from region to region along with nursery products that are traded between countries. Insects that damage trees include bark beetles, sucking insects, and defoliators. Bark beetles feed on a tree's inner bark. Sucking insects, such as aphids, suck the fluid from trees. Defoliators eat leaves and also attack evergreens. They include spruce budworms, tussock moths, and gypsy moths.

Foresters control diseases and pests by three chief methods: (1) biological controls, (2) silvicultural controls, and (3) direct controls. Biological controls fight diseases and pests with natural enemies. For example, foresters might spray a forest with a disease organism that affects a particular species of insect. Silvicultural controls use methods of timber management to make a forest undesirable for diseases and pests. For example, foresters may remove old, weak trees that are easy prey for fungi and insects. Direct controls include the use of chemical pesticides to kill fungi and insects. But the chemicals can kill nontarget plants and animals, and so pesticides are generally used only if other controls fail.

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Laws that protect U.S. forest resources. The United States government has often passed laws to protect forest resources. In 1911, the U.S. Congress passed the Weeks Law, which authorized the government to purchase forests that are part of watersheds for important rivers and streams. It also made federal funds available for states to fight forest fires on these lands. The Clarke-McNary Act of 1924 expanded the Weeks Law to cover fire protection of all forested land. It also allowed for the purchase and reforestation of land necessary for timber production. In 1947, Congress passed the Forest Pest Control Act. This law provided for federal cooperation with states and owners of private forests to control insect pests and diseases.

The Multiple Use-Sustained Yield Act was passed in 1960. It directed that national forests be managed in order to produce a sustained yield of timber and an adequate supply of other resources. In 1964, Congress passed the Wilderness Act, which provided for the preservation of wilderness areas in national forests and on other federal lands. No roads or buildings may be built in wilderness areas, and timber harvesting is forbidden. In 1974, the Forest and Rangeland Renewable Resources Planning Act was passed. It established procedures for continually reviewing the management of U.S. forests.

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History

People have relied on forest resources since prehistoric times. Many scientists believe deforestation led to the decline of many early civilizations. But throughout history, cultures learned to regulate the use of forests to prevent shortages of timber. During the Middle Ages, forest wildlife was protected to ensure a sufficient supply of game for the nobility to hunt. In the 1500's people in France and some German states began setting aside parts of forest plantations for timber cutting and other parts for growing new trees to replace those being used up. Forest management methods soon spread throughout Europe. In the 1700's and 1800's, the first colleges teaching forestry subjects opened in France and Germany. Further research helped shape forestry into a systematic and scientific approach to forest management.

In North America, the early settlers treated the vast timber resources as though they would last forever. They cleared much more land than they needed for their homes and crops and destroyed large areas of forestland by wasteful logging methods. By 1891, a conservation movement had started, and the U.S. Congress authorized the president to set aside wooded areas called forest reserves. The U.S. Forest Service was established in 1905. The service was given control of the forest reserves, which in 1907 became known as national forests. The Canadian Forest Service was established in 1899.

Since the mid-1900's, logging and the expansion of agriculture have damaged or cleared vast areas of the world's rain forests. Much of the deforestation has occurred in less developed nations as they have sought to secure short-term economic benefits. Worldwide conservation organizations have begun working with governments to promote sound management of tropical forests by the people who use them.

Today, researchers are seeking new ways to improve forestry practices. For example, methods involving the use of tissue cultures to develop seedlings using only a few cells are used to rapidly reproduce supertrees.

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